Filter media ribbons with nanofibers formed thereon

ABSTRACT

Nanofiber filter media ribbons are flexible elongate strips of polymeric material having a surface on which is formed an array of nanofibers. Ribbons are formable into woven or non-woven mats. The array of nanofibers can be configured to filter a predetermined contaminant from a fluid stream passing through the mats. Filter ribbons are formable by applying a moldable polymer to a first angular location of a rotating cylindrical roll having an array of nanoholes formed in a circumferential surface thereof so that the polymer covers the surface of the roll and infiltrates the nanoholes; cooling the polymer while rotating the polymer-covered roll to a second angular position; and removing the cooled polymer from the roll as an elongate film having an array of nanofibers formed on a surface thereof by the polymer that infiltrated the nanoholes.

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the reproduction of the patent document or the patentdisclosure, as it appears in the U.S. Patent and Trademark Office patentfile or records, but otherwise reserves all copyright rights whatsoever.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 16/941,364, filed Jul. 28, 2020 and entitled“FILTER MEDIA RIBBONS WITH NANOFIBERS FORMED THEREON”, which is adivisional of U.S. Non-Provisional patent application Ser. No.16/875,067, filed May 15, 2020 and entitled “FILTER MEDIA RIBBONS WITHNANOFIBERS FORMED THEREON”, which claims priority to U.S. ProvisionalPatent Application Ser. No. 62/852,970, filed May 24, 2019 and entitled“Unitary Multiscale Filter Media,” the entire disclosure of each ofwhich is hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX

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BACKGROUND OF THE INVENTION

The present disclosure relates generally to filter media and filterdevices, and more specifically to filter media and filter devices whichcombine user-defined arrays of nanofibers and elongate ribbon-likeelements to create filter media that provide the benefits of nanofibersin a form that can be utilized in ways similar to conventional filtermedia.

Fibrous filter media are used in various types of filter devices to traplarge and small particles in liquid and gas streams. Such filter mediaare typically formed from multiple layers of coarse and fine fibersextending parallel to an upstream surface of the filter media. An outerlayer of coarse fibers forms a bulk filtration layer for filtering oflarger particles, while an inner or underlying layer of fine fibersprovides filtering of small particles. Fine fibers are often provided ina thin layer laid down on a supporting permeable substrate or used withone or more permeable protective layers to obtain a variety of benefits,including increased efficiency, reduced initial pressure drop,cleanability, reduced filter media thickness, and to provide aselectively impermeable barrier to various liquids, such as water.However, prior approaches have several inherent disadvantages, includingthe need for a supporting substrate, a risk of delamination of the finefiber layer from the substrate, more rapid loading of the filter bycaptured particles, the alignment of fine fibers parallel to the mediaface surface, and an inability to control spacings between fine fibers.

In addition to filtering mechanisms, on the molecular level, fibrousmaterials also trap contaminants with electrostatic forces, includingionic bonding, hydrogen bonding, and Van der Waals forces. Theseelectrostatic interactions occur on the fiber surface. Because theseinteractions are known to increase non-linearly at sub-micron length(diameter) scales, functional improvement in fibrous filter media islargely based on minimizing denier (linear mass density or fiberdiameter). Although the production of filter media comprising very finefibers having a high surface-to-volume ratio, such as microfibers andnanofibers, has recently been emphasized in the industry, processinglimitations associated with traditional methods of producing such fiberslimit the utility of these materials in filtration applications.

The benefits realized through the use of nanofibers for filteringcontaminants from a fluid stream are well known, and the technology iswidely used. As currently commonly practiced, a thin layer ofelectrospun or melt-blown nanofibers is deposited on a porous substrate.Nanofibers deposited using these processes form a non-woven mat thatlacks physical strength. This makes handling of prior art nanofiber matswithout a suitable permeable substrate impractically difficult forfilter manufacturing. The unique filtering properties of a nanofiber matderive from the diameter of the nanofibers, and these properties arecurrently only obtainable with fibers formed into these non-wovenconstructs. Filter media formed of micro-fibers are easily handledduring filter manufacturing, but because of their larger diameter of thefibers lack the enhanced filtering abilities of nanofibers. Accordingly,to achieve these enhanced properties in a filter, nanofibers arecommonly deposited onto microfiber media in the manner previouslydescribed.

Nanofibers for prior art filter applications are commonly made byelectrospinning, a method that requires the use of high voltages and aflowing polymer solution containing solvents that evaporate duringproduction. Ensor, et al. in U.S. Pat. No. 8,652,229 describe methodsfor electrospinning nanofibers and forming filter elements therefrom. Inthe methods described, the electrospinning process requires electricalpotentials in the 25 kV to 30 kV range and the close control of severalprocess parameters. The rates of nanofiber production are low in theexamples given. It is not an environmentally friendly process due to thesolvents required. Electrospinning produces an interconnected web (ormat) of continuous small fibers with length to diameter ratios generally1,000,000:1 or greater.

When forming nanofibers by electrospinning, the nanofiber materials arelimited to polymers that can be mixed with a solvent to achieve theproperties required for the process.

In electrospinning the fibers of a closely controlled diameter aredeposited onto a substrate. The substrate may be a flat plate orientednormal to the axis of the origin of the solution stream. Alternatively,the substrate may be a rotating element with a cylindrical, conical orother radially symmetric shape, the axis of rotation being perpendicularto the axis of the solution stream. Or the substrate may be a rotatingdisc with the axis of rotation parallel to the axis of the solutionstream. Each of these substrate forms allow the forming of fiber matsconfigured to achieve specific design objectives through optimizing thedeposition pattern of the fibers. If translation of the substrate in aplane normal to the solution stream is added to any of the substrateconfigurations, the deposited fiber may be given a directionality.Indeed, the fiber mat may be formed with a predetermined pattern toachieve design objectives for a given application. Microfiber ornanofiber mats with a particular preferential orientation of the fibersare frequently referred to as “ordered”, and in some cases an “orderedmatrix”, or “ordered construct”. The “order” to which this refers, then,is that the elongate continuous fibers forming the mat do not have arandom directionality, but rather have a greater portion orientedparallel to a first axis than to a second axis. This is atwo-dimensional effect only since the fiber mat forms a thin sheet,frequently membrane-like.

Prior art nanofiber mats cannot withstand tensile loading. Becausenanofibers forming the mat have very low structural strength, increasingthe number nanofibers does not appreciably increase the thickness of themat, but simply creates a denser mat with decreased porosity. When thenanofiber mat manufactured by the electrospinning method is used to forman air filter, nanofibers (fibers) can be easily clogged (that is,packing can easily occur), resulting in a decrease in air permeabilityand an increase in pressure loss. Since clogging can easily occur, therehave been problems in that the pressure loss may easily increase and theservice life of an air filter may be shortened.

To address these drawbacks, Konishi, in US Application Publication2018/0353883 discloses an alternate method (not electrospinning) forforming a non-woven mat of nanofibers. Konishi's method forms a mat offibers that have a range of diameters that average less than one micron,but also that also contains fibers of larger diameters so as to give themat increased thickness and spacing between the nanofibers. The numberof fibers having fiber diameters ranging from 2 times up to 10 times theaverage fiber diameter of the constituent fibers is in a range of 2 to20% of a total number of the constituent fibers. The fiber mat isdeposited onto a non-woven fabric using a complex process. Although thethickness of the mat is somewhat increased, the long continuous fibersare randomly deposited in a two-dimensional construct similar toelectrospun mats.

Microfibers for filters and other applications may be made by meltblowing, a fiber making process in which melted polymer is extrudedthrough a plurality of small orifices surrounded by streams of a highvelocity gas. A plurality of randomly oriented fibers are deposited ontoa substrate so as to form a non-woven mat or fabric. The process doesnot require the use of solvents or high voltages, and the fiberdeposition rates can be orders of magnitude greater than those possibleby electrospinning. Melt blown fibers are generally in the range of twoto five microns with a wide diameter distribution. Because the fibersare not drawn to a substrate by an electrostatic charge as inelectrospinning, fiber mats formed by melt blowing are notmembrane-like, but rather have fibers that are spaced one from anotherin the direction parallel to the blowing direction. The fibers are longand continuous with a random orientation. In some applications the matis subsequently compressed to form a non-woven fabric. Melt blowingnanofibers is difficult since extremely small orifices are required andthe molten plastic must flow through these orifices and remain in fiberform as they travel to the substrate. Surface tension in the moltenfiber tends to cause the material to become droplets rather than fibersso as to reduce the surface energy. Accordingly, the polymers that canbe successfully melt blown into nanofibers is limited and the processhas not yet been scaled up sufficiently for commercial use. The processremains an efficient method for forming microfiber mats and non-wovenfabrics for filters and other applications.

In another approach, increasing the nanofiber content of a filter isaccomplished through the use of a stratified filter construction withlayers of nanofibers interspersed between microfiber substrate layers.

Whether a nanofiber mat is formed by electrospinning, Konshi's method,or another means, the mat is a thin construct, frequently membrane-like.Because of this, the mat is oriented essentially normal to the flowstream direction. The density of the mat is limited by the backpressurethat the filtering process can tolerate.

The beneficial effects of including nanofibers in a filter may betemporarily enhanced by electrostatically charging the nanofibers. Forinstance, it has been demonstrated that charging nanofiber matsinterspersed between insulating separating permeable layers causes asignificant increase in the filter efficiency. This is described indetail in US application publication 2019/0314746 by Leung. However, theapplied electrostatic charge degrades over time so that filters of thistype have a finite shelf life, making them impractical for someapplications.

Polymeric materials have an inherent electrostatic charge that createsan attractive force, the force at any given point on a surface beinginversely dependent on the radius of curvature of the external surfaceat that point. When the radius of curvature is large the electrostaticattractive force is weak. As the radius is decreased the attractiveforce increases, a factor exploited in nanofiber filter media. The smalldiameter of the nanofibers results in an attractive force that is ordersof magnitude greater than that of microfibers allowing nanofibers todraw contaminant particles with greater force for removal from a fluidstream. This electrostatic charge is intrinsic to the material and doesnot degrade in the manner of an applied electrostatic charge.

Filters for use in personal protective equipment (PPE) may also benefitfrom the inclusion of nanofibers. Specifically, face masks that form atight seal to the face, also referred to as respirators, are commonlyused to prevent contaminants from entering the airway of the wearer.These devices reduce the wearer's exposure to particles including smallparticle aerosols and large droplets. Face masks of this type mustremove contaminants while minimizing the pressure drop across the filterelement. The filtering element forming the mask my also be pliable so asto allow the mask to form a seal with the face of the wearer. Typicallya wearable filter of this type will have a permeable hydrophobic outerprotective layer, a coarse filter media layer for removing largeparticulate, a fine filter medial layer for removing smallerparticulate, and an inner soft permeable fabric layer for contacting theface of the wearer.

Leung in U.S. Pat. No. 8,303,693 teaches a face mask that incorporates afiltration medium a fine filter layer having a plurality of nanofibersand a coarse filter layer having a plurality of microfibers attached tothe fine filter layer. Flow passes through the coarse filter to the finefilter layer. The polymer nanofibers in the fine filter layer may beobtained in a variety of ways including electrospinning or bymelt-blowing. Accordingly, the nanofibers are long and continuous with arandom orientation. The thickness of this nanofiber layer may have athickness of about 0.01 to about 0.2 millimeters. Because the nanofiberfine filter layer is a thin layer, the layer may tend to clog easily andincrease the resistance to air flow. The coarse and fine layers togetherform a “well-bonded laminate structure”, the layers being bonded one toanother. Indeed, it is necessary for the nanofiber layer to be bonded tothe microfiber layer for handling purposes during manufacture of afilter since the nanofiber layer lacks physical strength. In oneembodiment the nanofibers are deposited onto the microfiber layer duringelectrospinning or melt blowing so that they adhere to the microfiberlayer. In another embodiment the nanofibers are deposited onto a liquidin which the microfibers are submerged so that the nanofibers are notadhered to the microfibers. When forming of a nanofiber layer iscomplete, the liquid is removed leaving the nanofiber layer atop themicrofiber layer but not adhered thereto. The nanofiber layer andmicrofiber layer are then compressed mechanically together with a smallamount of compatible adhesive to form a rigid structure. The manner inwhich Leung's layered filter assembly is formed illustrates thedifficulty and limitations of forming filter assemblies incorporatingelectrospun and melt blown nanofibers due to their mechanicalproperties. As with other applications that incorporate electrospunnanofibers, the fiber making process is difficult to scale up and isenvironmentally undesirable due to the solvents used. The integration ofnanofibers into a mask assembly is similarly difficult.

Hofmeister, et al. in U.S. Pat. No. 10,159,926 teaches media and devicesfor filtering or separating a contaminant from a fluid liquid or gasstream. The Hofmeister devices incorporate flow passages formed bylayered laminas comprising tunable topographies of user-defined arraysof nanofibers and, optionally, nanoholes. These tunable nanofibertopographies selectively remove contaminants from the fluid stream as itflows through spaces between adjacent laminas, parallel to the surfaceof the laminas, with at least one of these surfaces having nanofibersformed thereon. Contaminants are drawn to the nanofibers byelectrostatic forces in the manner previously described. Nanofiberfilters constructed in accordance with the Hofmeister patent can betuned to remove specific contaminants such as pathogens, chemicalcontaminates, biological agents, and toxic or reactive compounds from afluid to be filtered by selecting a suitable nanofiber diameter, height,distance between nanofibers, interlaminar gap and material.

The Hofmeister filter construction requires a rigid housing to maintainthe orientation and alignment of the laminas making up the filter sothat a continuous flow path is created between an inlet and outletformed in the housing, the flow passing through interlaminar spacesformed therein.

Accordingly applications for the Hofmeister filter with its tunedtopography are limited to those in which the fluid stream is directedthrough spaces formed between adjacent, aligned laminas, the alignmentbeing maintained by a rigid housing structure. Because of this, thebenefits of filter elements comprising a tuned topography formed ofnanofiber arrays cannot be realized in filtering devices that donot/cannot include a rigid housing and flow between adjacent parallellaminas.

There is a need for filter media that exploit the inherent electrostaticproperties of nanofibers in optimized configurations that do not requirea rigid housing and laminar construction. Such media are the subject ofthis invention.

Accordingly, it is an object of the present invention to providenanofiber filter media that can withstand tensile loading.

It is also an object of the present invention to provide nanofiberfilter media that achieve high collection efficiency and reducedclogging (packing) between fibers.

It is also an object of the present invention to provide nanofiberfilter media that does not require deposition on a substrate duringmanufacture.

It is also an object of the present invention to provide nanofiberfilter media wherein the nanofibers are configured to optimally exploitthe electrostatic properties of the nanofibers.

It is also an object of the present invention to provide nanofiberfilter media wherein the nanofibers cannot be easily expelled from thefilter media.

It is also an object of the present invention to provide nanofiberfilter media wherein the nanofibers are integrated in a heterostructurecontaining nanofibers and support.

It is further an object of the present invention to provide nanofiberfilter media at lower cost than current nanofiber media.

It is further an object of the present invention to provide nanofiberfilter media that may be produced without the need for high voltages orenvironmentally detrimental solvents.

It is also an object of this invention to provide a method forincreasing the wettability of a fluid on a surface of filter mediathrough the formation of nanofibers on one or more surfaces of themedia.

It is further an object of this invention to provide a method fordecreasing the wettability of a fluid on a surface of filter mediathrough the formation of nanofibers on one or more surfaces of themedia.

It is an object of this invention to provide a method of selectivelyincreasing the wettability of a surface of a filter media for a firstflow stream component while decreasing the wettability for a second flowstream component.

It is finally an object of this invention to provide nanofiber filtermedia that can remove biological contaminants including viruses from anair stream

BRIEF SUMMARY

These and other objects are achieved in devices and methods of thepresent invention which addresses filter media, filtering devices formedtherefrom, and methods for their use wherein the filter media is formedof flexible, elongate ribbon-like polymeric elements having arrays ofnanofibers formed thereon. These ribbon elements and ribbon segments maybe formed by cutting, slicing, chopping, or slitting elongate filmelements on which are formed nanofiber arrays. Ribbons so formed have aplanar portion of predetermined thickness and width that may be formedto other non-planar shapes in subsequent processing. These media ribbonsmay also be formed by embossing of the nanofiber arrays on monofilamentfibers as well as on woven and non-woven fiber assemblies. Devices andmethods of the present invention are not limited by the method ofmanufacture of the elongate ribbon-like elements.

The elongate ribbons of filter media of the present invention are formedof a suitable polymeric film, have a flexible planar portion ofpredetermined thickness and width, and have an array of nanofibersformed on at least one surface of the film. In a preferred embodimentthe nanofibers are arranged in rows spaced a first distance apart, withthe nanofibers within each row spaced a second distance apart. In someembodiments the first and second distances are equal. In others they arenot. The diameter of each nanofiber generally decreases along thenanofiber's length from a first diameter at its base, and the lengths ofthe fibers in an array fall within a predetermined range. The form of afiber is largely determined by the ratio of the length of the fiber toits diameter. At low ratios the fiber may have a post-like appearance,while at high ratios the fiber may be tendrilous. Between these extremesis a continuum of nanofiber configurations that share the commoncharacteristic of decreasing diameter over their finite length. Becausethe electrostatic force at a point on a surface is inversely related tothe radius of curvature of the surface at that point, the electrostaticforce on a nanofiber of filter media of the present invention is notconstant along its length. The electrostatic force increases with thedistal reduction in diameter, reaching its maximum at the fiber's distalend. In certain embodiments the ends of the nanofibers are configured tofurther enhance the electrostatic potential. The electrostatic force ofnanofibers formed on ribbon media of the present invention has maximalintensity at the distal portions of the nanofibers—the portion that ismost exposed to the fluid stream. This concentration results in muchhigher attractive forces to contaminants in the fluid stream than theuniform-diameter, continuous fibers of non-woven nanofiber matspreviously herein described and currently in use in filter applications.Because of this, nanofiber arrays formed on filter ribbons of thepresent invention are able to draw contaminants from a flow stream withhigher field gradients than other, prior art, nanofiber filter elements.

As with suitably constructed prior art filters, an electrostatic chargemay be imparted to the filter media of the present invention to increasethe attractive force of the nanofiber arrays formed on ribbons. Incertain embodiments, filter ribbons of the present invention are formedfrom a polymer or polymer blend with suitable electret properties. Amongthese materials are polypropylene, poly(phenylene ether) (PPE) andpolystyrene (PS) and others. In certain embodiments these ribbons have alamellar construction wherein a first layer on which are formednanofiber arrays of the present invention is bonded to a second layerwith optimal physical and/or electrical properties, the first layerbeing formed of a suitable electret material. Charging of the media maybe accomplished by corona discharge, triboelectrification, polarization,induction, or another suitable method. The imparted electrostatic chargemay be dissipated by particle loading, and/or by quiescent or thermalstimulation decay.

In certain embodiments filter media ribbons of the present invention areformed of an antimicrobial plastic. One such material, MICROBAN® byMicroban, Inc. (Huntersville, N.C.) is a synthetic polymer materialcontaining an integrated active ingredient which makes it effectiveagainst microbial growth. In certain embodiments these ribbons have alamellar construction wherein a first a layer on which are formednanofiber arrays of the present invention is bonded to a second layerwith optimal physical properties, the first layer being formed of aantimicrobial plastic. Antimicrobial agents may be blended with polymerswith optimal properties for forming nanofiber arrays in methods hereindescribed to create filter ribbons of the present invention that notonly have the ability to efficiently remove microbes from a fluidstream, but also to kill those microbes.

The non-random placement of nanofiber tips in a nanofiber arrayrepresents a significant enhancement over nanofiber structures producedby other methods, such as electrospinning, because each fiber forming anarray of nanofibers described herein has an independent “end” or “tip.”The “ends” or “tips” of the nanofibers have stronger field gradientsthan the body of the fibers because gradients are enhanced withcurvature and the curvature is highest at the tip. Thus, the use infilter devices of nanofiber arrays having millions of tips per squarecentimeter of lamina surface preserves and enhances the local fiberfield gradient far better than traditional fibrous filter media anddevices which rely on layered mats of fibers laid down on a substrate.

Because the electrostatic forces are generated by nanofibers formed onthe surface of media ribbons of the present invention, the width andthickness of the ribbon on which the nanofiber arrays are formed may beselected based on physical strength, handling, flow or other factorssince it does not affect the electrostatic properties of the nanofibersformed thereon. Because the ribbons have appreciable physical strength,structures formed of them may be handled independent of a substrate, andindeed, make practical woven and non-woven mats that may be incorporatedin a wide range of filter configurations. Non-woven mats formed of theribbons may be integrated into a single assembly by bonding of theribbons one to another using a suitable bonding method. For applicationsin which the filter must flexibly conform to an external surface, anon-woven mat of bonded or loose ribbons may be positioned between firstand second porous or permeable sheet materials and secured there byfastening means between the porous sheets. The sheets may be joined bystitching, needling or other mechanical means, thermal bonding, chemicalbonding or other suitable joining method. In a preferred embodiment aquilted assembly is formed by the permeable sheets and the nanofiber matpositioned therebetween, stitching serving to maintain the positions ofthe elements. In a preferred embodiment one or both of the permeablesheets are formed of filter media. In a preferred embodiment one or bothsheets themselves incorporate nanofiber arrays so as to impart specificwettability properties. For instance, a permeable sheet may be nominallywetted by a first selected liquid or vapor while nominally not wetted bya second selected liquid or vapor. Filter media ribbons of the presentinvention may be weaved to create flexible filter structures. Individualribbons may be weaved to form the structure, or the ribbons may beformed into a yarn prior to weaving. The tightness of the yarn and ofthe woven structure may be optimized to achieve desired flowcharacteristics.

Elongate ribbons of the present invention with the nanofibers formedthereon may be subsequently processed in the same manner as otherconventional fibrous media. Because of this, nanofiber filter media ofthe present invention may be formed into or integrated into filterelements at much lower cost and with much greater design flexibilitythan prior art, conventionally formed nanofibers made by electrospinningor other similar process.

While prior art nanofiber mats formed by electrospinning or othermethods form a thin, membrane-like structure, mats formed of filterribbons of the present invention are three-dimensional constructs.Ribbons may be piled on top of other ribbons to create mats of a desiredthickness, or may fill a cavity through which the fluid stream flows.Mats formed of filter media ribbons of the present invention areflexible and resilient. Their pliable nature and low resistance to fluidflow make mats of the present invention ideally suited for use inpersonal protective filtering devices used in medical and industrialapplications.

A respirator mask of the present invention has a layered filterconstruct includes filter ribbons of the present invention and benefitsfrom the unique properties of the ribbons. A first, external (distal)layer is a thin woven or non-woven mat (fabric) formed of filter ribbonsof the present invention, the ribbons being made of a hydrophobicpolymeric material. On a surface of each of these ribbons are formedarrays of nanofibers configured to optimally increase the hydrophobiccharacteristics of this exterior fabric. Proximal to this first layer isa second layer formed of microfibers configured to remove largeparticulate. Optionally this second layer may also contain nanofiberbearing filter ribbons of the present invention with the nanofiberarrays configured to optimally remove contaminants of a firstcomposition or size. Proximal to this second layer is positioned a thirdlayer. This layer is a non-woven mat formed of nanofiber bearing filterribbons of the present invention. Because the ribbons from which thislayer are formed have structural strength, the non-woven mat has apredetermined thickness and flow characteristics selected for optimalremoval of contaminants while preserving airflow at low pressure dropand resistance to clogging. The arrays of nanofibers on these ribbonsare optimally configured for the removal of small particles. In certainembodiments nanofiber arrays of ribbons forming this third layer may beconfigured to preferentially remove specific contaminants. Indeed,additional layers of ribbon mats of the present invention may bepositioned proximal to this third layer, the nanofiber arrays of eachlayer being optimized to remove specific contaminants. Proximal to thepreviously described filter layers is a permeable fabric, woven ornon-woven that may, in some embodiments, be comfortably pressed againstthe face of the wearer. In production, the layers forming the filterassembly may be produced as continuous sheets of material, laid up inthe proper order, and maintained in their relative position. Elements ofthe construct may be fastened together in selected locations thermally,by a glue or solvent bonding, by stitching, or by needle punch, ajoining method for non-woven fabrics. Because nanofibers of the presentinvention are integrally formed on the surface of ribbons of the presentinvention, the nanofibers cannot become loose and be inhaled by thewearer as is possible with respirators made with prior art filterassemblies.

In certain embodiments the film portion of nanofiber media ribbons ofthe present invention remain smoothly, flexibly planar or curvilineardepending on forces applied thereto. In other embodiments the filmportion may be crinkled, that is, may have wrinkles or ripples formedtherein so as create flow spaces between ribbons when they are assembledinto a woven or non-woven mat. Alternatively, a ribbon may be twisted soas to ensure that there are flow spaces between adjacent ribbons in amat. While heretofore nanofiber media have been described with referenceto elongate ribbons, in certain embodiments, the ribbons are choppedinto short segments prior to forming a bed of loose or bonded ribbonsfor integration into a filter assembly.

The orientation of media ribbons of the present invention relative tothe fluid stream in a filter assembly may be random or may have a degreeof preferential orientation. That is, the ribbon surfaces with nanofiberarrays formed thereon may be randomly presented to the fluid flow, ormay be oriented so that preferentially the surfaces primarily face theoncoming flow, or are primarily oriented parallel to the flow direction.

Filter media ribbons of the present invention with their nanofiberarrays are formed without the use of solvents or high voltage.Specifically, nanofiber arrays of the present invention are formed in acasting process in which a suitable polymer heated to a temperaturesufficient to allow flow, is extruded onto a first surface of a moldwith an array of nanoholes formed therein, and subsequently flows intothe nanoholes of the mold. A surface of a second compressing orquenching element may be used. Subsequently, the polymeric material iscooled sufficiently so that when the compressing element is removed, thepolymer with the attached molded nanofibers can be stripped from themold surface. The result is a planar polymeric film portion with anarray of nanofibers integrally formed on a first surface thereof, theform of the nanofiber array being complementary to nanohole array in themold. The first surfaces of the mold and compressing element may beplanar with the polymeric material introduced therebetween as a filmprior to heating and material flow into the mold nanoholes.Alternatively, the mold and second element may be rotating cylinders,the polymer in molten form being introduced onto the circumferentialsurface of the mold, and subsequently compressed between the mold andthe cylindrical surface of the second element. This compression enhancesthe cooling the material so that it can be subsequently peeled from themold. Whether formed in discrete segments as when using a mold of planargeometry, or formed as elongate strips using the rotating cylindricalmold, the resulting film with arrays of integral nanofibers formedthereon may be cut, slit, chopped or otherwise divided into filter mediaribbons of the present invention.

In some embodiments the filter media ribbons are formed of a singlepolymeric material. Others have a layered construction comprising two ormore polymeric materials that together give the filter ribbons anoptimal combination of filtering properties for a given application, andphysical properties for manufacture of the ribbons. For instance,nanofiber arrays of a first material may be laminated to a film of asecond material with optimal mechanical properties that is formedseparately. In a variation of the previously described casting methodfor producing film whereon are formed arrays of nanofibers, rather thanapplying molten polymer to the mold, a polymer film is applied to themold. The film is then heated to a temperature sufficient to melt orsufficiently soften the material so as to allow the material to flowinto nanoholes in the mold. The surface of a compressing element mayincrease flow of the material into the nanoholes. The polymer is thencooled sufficiently to allow the film with nanofibers formed thereon tobe stripped from the mold. As with the previously described castingprocess, nanofiber bearing films for fiber ribbons of the presentinvention formed using this method may have a layered construction, asecond film being compressed against the first, nanofiber forming filmby the compressing element so that the films are bonded one to another

Numerous other objects, advantages and features of the presentdisclosure will be readily apparent to those of skill in the art upon areview of the following drawings and description of exemplaryembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with referenceto the following figures, wherein like reference numerals refer to likeparts throughout the various drawings unless otherwise specified. In thedrawings, not all reference numbers are included in each drawing, forthe sake of clarity.

FIG. 1A is a perspective schematic representation of a chill rollcasting system for making nanofiber filter elements of the presentinvention.

FIG. 1B is an expanded view of the objects of FIG. 1A at location A.

FIG. 1C is an expanded view of the objects of FIG. 1A at location B.

FIG. 1D is a second perspective schematic representation of the chillroll casting system of FIG. 1A.

FIG. 2A is a perspective view of a ribbon element of nanofiber filtermedia of the present invention.

FIG. 2B is a plan view of the objects of FIG. 2A.

FIG. 3 is a side elevational view of the objects of FIG. 2A.

FIG. 4 is an expanded view of the objects of FIG. 2A at location C.

FIG. 5 is an expanded view of the objects of FIG. 2B at location B.

FIG. 6 is an expanded view of the objects of FIG. 3 at location A.

FIG. 7 is an expanded view of the objects of FIG. 6 at location D.

FIG. 8 is a side elevational view of an alternate embodiment nanofiberof filter media of the present invention.

FIG. 9 is a side elevational view of the nanofiber of FIG. 7 depictingthe electrostatic field surrounding the nanofiber.

FIG. 10 is a side elevational view of the nanofiber of FIG. 8 depictingthe electrostatic field surrounding the nanofiber.

FIG. 11 is a side elevational sectional view of a planar polymericelement wherein a first portion of a planar surface comprises ananofiber array of the present invention and a second portion does not.

FIG. 12A depicts the polymeric element of FIG. 11 with liquid applied toeach portion wherein the nanofibers increase the wettability of thesurface.

FIG. 12B depicts the polymeric element of FIG. 11 with liquid applied toeach portion wherein the nanofibers decrease the wettability of thesurface.

FIG. 13 depicts a nonwoven mat of nanofiber bearing ribbon elements ofthe present invention.

FIG. 14A depicts a personal filter mask formed with nanofiber filtermedia of the present invention.

FIG. 14B depicts the layered structure of the mask of FIG. 14A atlocation A.

FIG. 15 is a sectional view of a composite filter media assemblyincluding elongate filter ribbons of the present invention.

FIG. 16A is a perspective depiction of an alternate embodiment filterribbon of the present invention.

FIG. 16B is an expanded view of the objects of FIG. 16A at location A.

FIG. 17A is a perspective depiction of another alternate embodimentfilter ribbon of the present invention.

FIG. 17B is an expanded view of the objects of FIG. 17A at location A.

FIG. 18 is a perspective schematic representation of a chill rollcasting system for making nanofiber filter elements of the presentinvention configured for directly producing filter ribbons of thepresent invention.

FIG. 19 is an expanded view of the objects of FIG. 18 at location A.

FIG. 20 is a perspective schematic representation of a chill rollcasting system for making nanofiber filter elements of the presentinvention configured for directly producing filter ribbon segments ofthe present invention.

FIG. 21 is an expanded view of the objects of FIG. 20 at location A.

FIG. 22 is a perspective view of a filter ribbon segment of the presentinvention.

FIG. 23 is a plan view of the objects of FIG. 22.

FIG. 24 is a side elevational view of the objects of FIG. 22.

FIG. 25 is a perspective view of an alternate embodiment filter ribbonsegment of the present invention.

FIG. 26 is a plan view of the objects of FIG. 25.

FIG. 27 is a side elevational view of the objects of FIG. 25.

FIG. 28 is a perspective schematic representation of an alternateembodiment chill roll casting system for making nanofiber filterelements of the present invention, configured for producing nanofiberbearing film wherein a nanofiber bearing layer of a first material isbonded to a film of a second material.

FIG. 29 is a side elevational view of the objects of FIG. 28.

FIG. 30 is an expanded view of the objects of FIG. 29 at location B.

FIG. 31 is an expanded view of the objects of FIG. 28 at locaton A.

FIG. 32 is a perspective view of an alternative method system forproducing nanofiber bearing filter ribbons of the present invention.

FIG. 33 is a side elevational view of the objects of FIG. 32.

DETAILED DESCRIPTION

The details of one or more embodiments of the presently disclosedsubject matter are set forth in this document. Modifications toembodiments described in this document, and other embodiments, will beevident to those of ordinary skill in the art after a study of theinformation provided herein. The information provided in this document,and particularly the specific details of the described exemplaryembodiments, is provided primarily for clearness of understanding and nounnecessary limitations are to be understood therefrom. In case ofconflict, the specification of this document, including definitions,will control.

The present disclosure relates to filter media and devices for removinga contaminant from a fluid stream. In a general embodiment, thenanofiber filters disclosed herein are designed to filter a substance orcontaminant from a fluid stream using one or more user-defined arrays ofnanofibers, such as those described in U.S. 2013/0216779 which isincorporated herein by reference in its entirety.

While the terms used herein are believed to be well understood by one ofordinary skill in the art, definitions are set forth herein tofacilitate explanation of the subject matter disclosed herein.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the subject matter disclosed herein belongs. Althoughany methods, devices, and materials similar or equivalent to thosedescribed herein can be used in the practice or testing of the presentlydisclosed subject matter, representative methods, devices and materialsare now described.

The terms “a”, “an”, and “the” refer to “one or more” when used in thisapplication, including the claims. Thus, for example, reference to “acontaminant” includes a plurality of particles of the contaminant, andso forth. The use of the word “a” or “an” when used in conjunction withthe term “comprising” in the claims and/or the specification may mean“one,” but it is also consistent with the meaning of “one or more,” “atleast one,” and “one or more than one.”

All references to singular characteristics or limitations of the presentdisclosure shall include the corresponding plural characteristic(s) orlimitation(s) and vice versa, unless otherwise specified or clearlyimplied to the contrary by the context in which the reference is made.

All combinations of method or process steps as used herein can beperformed in any order, unless otherwise specified or clearly implied tothe contrary by the context in which the referenced combination is made.

The methods and devices of the present disclosure, including componentsthereof, can comprise, consist of, or consist essentially of theessential elements and limitations of the embodiments described herein,as well as any additional or optional components or limitationsdescribed herein or otherwise useful.

This description and appended claims include the words “below”, “above”,“side”, “top”, “bottom”, “upper”, “lower”, “when”, “upright”, etc. toprovide an orientation of embodiments of the invention to allow forproper description of example embodiments. The foregoing positionalterms refer to the apparatus when in an upright orientation. A person ofskill in the art will recognize that the apparatus can assume differentorientations when in use. It is also contemplated that embodiments ofthe invention may be in orientations other than upright withoutdeparting from the spirit and scope of the invention as set forth in theappended claims. Further, it is contemplated that “above” means havingan elevation greater than, and “below” means having an elevation lessthan such that one part need not be directly over or directly underanother part to be within the scope of “above” or “below” as usedherein.

The phrase “in one embodiment,” as used herein does not necessarilyrefer to the same embodiment, although it may. Conditional language usedherein, such as, among others, “can”, “might”, “may”, “e.g.,” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states.

Unless otherwise indicated, all numbers expressing physical dimensions,quantities of ingredients, properties such as reaction conditions, andso forth used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thisspecification and claims are approximations that can vary depending uponthe desired properties sought to be obtained by the presently disclosedsubject matter.

As used herein, the term “about,” when referring to a value or to anamount of mass, weight, time, volume, concentration, percentage or aphysical dimension such as length, width, or diameter, is meant toencompass variations of in some embodiments +−40% or more, in someembodiments +−20%, in some embodiments +−10%, in some embodiments +−5%,in some embodiments +−1%, in some embodiments +−0.5%, and in someembodiments +−0.1% from the specified value or amount, as suchvariations are appropriate to perform the disclosed methods.

As used herein, ranges can be expressed as from “about” one particularvalue, and/or to “about” another particular value. It is also understoodthat there are a number of values disclosed herein, and that each valueis also herein disclosed as “about” that particular value in addition tothe value itself. For example, if the value “10” is disclosed, then“about 10” is also disclosed. It is also understood that each unitbetween two particular units are also disclosed. For example, if 10 and15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

As used herein, the term “fluid” is defined as any liquid or gas whichcan be passed through the filter media and filter devices disclosedherein. Multiple fluids having different specific gravities andviscosities can be used as well as gas and vapor streams, depending onthe application.

As used herein, the term “nanofiber” refers to a fiber structure havinga diameter of less than 1000 nanometers for more than half the length ofthe structure. In some embodiments, the nanofibers disclosed herein cancomprise a tapered base portion and a relatively longer fiber portionwhich extends from the base portion. In such embodiments, the fiberportion has a diameter of less than 1000 nm and a length greater thanthat of the base portion, and the base portion can have a diameter offrom about 10 micron to less than 1.0 micron. Additionally, in someembodiments, the base portion can also have a length of from about 1.0micron to about 10 microns, and the fiber portion can have a length offrom about 10 to 100 times greater than the length of the base portion.Nanofibers having larger diameter base portions in the range of fromabout 2.0 microns to about 10 microns are best suited for applicationswherein the bases must provide stiffness to the nanofiber in the fluidstream.

In some preferred embodiments, nanofibers suitable for use in thenanofiber filter media and filter devices disclosed herein can have anoverall length of from about 10 to about 100 microns. Accordingly,suitable nanofibers can also have a length to diameter ratio of from10:1 to about 1000:1. In one embodiment, the length to diameter ratio isfrom about 10:1 to about 100:1. By contrast, nanofibers known in theart, including electrospun nanofibers, melt-blown nanofibers andmicrofiber-derived nanofibers (i.e., microfibers split during processingto obtain sub-micron diameter structures), typically have much greaterlength to diameter ratios in the range of 1,000,000:1 to 100,000,000:1.As a result, the nanofibers used in nanofiber filter media and filterdevices disclosed herein can have from about 10 to about 1000 times moretips per unit length than electrospun nanofibers, melt blown nanofibersand microfiber derived nanofibers.

The related terms “nanofiber array” and “array of nanofibers,” which areused interchangeably herein, collectively refer to a plurality offreestanding nanofibers of user-defined physical dimensions andcomposition integrally formed on and extending from a backing member,such as a film, according to user-defined spatial parameters. In someembodiments, the nanofiber arrays disclosed herein include nanofiberswhich extend from a surface of the backing member at an anglesubstantially normal to a plane containing the surface of the backingmember from which the nanofibers extend. By contrast, electrospunnanofibers, melt-blown nanofibers, and microfiber-derived nanofibers areneither integrally formed on nor do they extend from a backing member.

User-tunable physical characteristics of the nanofiber arrays disclosedherein include fiber spacing, diameter (also sometimes referred toherein as “width”), height (also sometimes referred to herein as“length”), number of fibers per unit of backing member surface area(also referred to herein as “fiber surface area density”), fibercomposition, fiber surface texture, and fiber denier. For example,nanofiber arrays used in the filter media and filter devices disclosedherein can comprise millions of nanofibers per square centimeter ofbacking member, with fiber diameter, length, spacing, materialcomposition, and texture configured to perform a filtration function. Insome embodiments, one or more of fiber surface area density, diameter,length, spacing, composition, and texture are controlled and optimizedto perform a filtration function. In certain embodiments, the nanofiberarrays can be optimized or “tuned” to perform a specific filtrationfunction or target a preselected substance or specific retentate. Infurther embodiments, an array of nanofibers disposed on a portion of afilter lamina forming a flow passage of a filter device disclosed hereinis configured to filter a substance from a fluid containing thesubstance when the fluid is flowed through the flow passage.

The nanofiber arrays disclosed herein, when formed on a substantiallyplanar surface of a backing member, can include nanofibers spaced alongan X-axis and a Y-axis at the same or different intervals along eitheraxis. In some embodiments, the nanofibers can be spaced from about 100nm to 200 micron or more apart on the X-axis and, or alternatively, theY-axis. In certain embodiments, the nanofibers can be spaced from about1 micron to about 50 micron apart on one or both of the X-axis and theY-axis. In a preferred embodiment, the nanofibers can be spaced fromabout 2 micron to about 7 micron apart on one or both of the X-axis andthe Y-axis.

In some embodiments, an array of nanofibers can include nanofibershaving an average length of at least 25 micron. In certain embodiments,the nanofibers can have a length of from about 10 micron to about 100micron. In certain embodiments, the nanofibers can have a length of fromabout 15 micron to about 60 micron. In an exemplar embodiment, thenanofibers can have an average length of from about 20 micron to about30 micron. In specific embodiments, the nanofibers can have a length ofabout 15.00 micron, 16.00 micron, 17.00 micron, 18.00 micron, 19.00micron, 20.00 micron, 21.00 micron, 22.00 micron, 23.00 micron, 24.00micron, 25.00 micron, 26.00 micron, 27.00 micron, 28.00 micron, 29.00micron, 30.00 micron, 31.00 micron, 32.00 micron, 33.00 micron, 34.00micron, 35.00 micron, 36.00 micron, 37.00 micron, 38.00 micron, 39.00micron, 40.00 micron, 41.00 micron, 42.00 micron, 43.00 micron, 44.00micron, 45.00 micron, 46.00 micron, 47.00 micron, 48.00 micron, 49.00micron, 50.00 micron, 51.00 micron, 52.00 micron, 53.00 micron, 54.00micron, 55.00 micron, 56.00 micron, 57.00 micron, 58.00 micron, 59.00micron, or 60.00 micron.

The nanofiber backing member surface area density can range from about25,000,000 to about 100,000 nanofibers per square centimeter. In someembodiments, the nanofiber surface area density can range from about25,000,000 to about 2,000,000 nanofibers per square centimeter. Inspecific embodiments, the nanofiber surface density is about 6,000,000nanofibers per square centimeter. In an exemplar embodiment, thenanofiber surface area density is about 2,000,000 nanofibers per squarecentimeter.

In some embodiments, an array of nanofibers can include nanofibershaving an average denier of from about 0.001 denier to less than 1.0denier. In an exemplar embodiment, the nanofibers forming a nanofiberarray disclosed herein can be less than one denier and have a diameterranging from about 50 nm to about 1000 nm.

Nanofiber arrays and methods for producing nanofiber arrays suitable foruse in the filter media and filter devices disclosed herein aredescribed by the present inventors in U.S. 2013/0216779, U.S.2016/0222345, and White et al., Single-pulse ultrafast-laser machiningof high aspect nanoholes at the surface of SiO2, Opt. Express.16:14411-20 (2008), each of which is incorporated herein by reference inits entirety.

A preferred method for manufacturing herein described ribbons and ribbonsegments of the present invention with nanofiber arrays for filterelements of the present invention is hot pressing, a method in which asuitable polymeric film is positioned between a temperature controlledcompressing plate and a substrate/mold formed of silica or anothersuitable material in which patterns of nanoholes have been formed, thepattern of the nanoholes being complementary to the pattern ofnanofibers to be produced. Methods for making molds with patterns ofnanoholes formed therein by single-pulse femto-second laser machiningare described in detail in US 2015/0093550, herein incorporated byreference in its entirety. The compressing plate, mold and film areheated to a predetermined temperature and a force is applied to thecompressing plate so as to press the film against the silica mold. Whenthe temperature of the film material reaches a sufficient level, thesoftened film material flows into the nanoholes in the mold. In someembodiments with certain materials the softened polymer infiltrates thenanoholes due to surface tension effects only. In other embodiments withfilms formed of the same or different materials, infiltration of thenanoholes is accomplished by a combination of hydrostatic pressure andsurface tension. Thereafter the system is cooled sufficiently to allowthe film to be peeled off of the substrate with the molded nanofibersattached to its first surface. The hot-pressing method for producingfilter ribbons with nanofiber arrays is described in detail byHofmeister, et al. in US 2016/0222345, herein incorporated by reference.While hot pressing is a preferred method for forming ribbons for filtersof the present invention, solution casting may also be used. Thesolution casting method for producing filter ribbons with nanofiberarrays is described in detail by Hofmeister, et al. in US 2015/0093550.

Another preferred method for manufacturing ribbons of the presentinvention has the ability to produce continuous elongate strips of filmwith arrays of nanofibers formed on at least one surface thereof. Inmethod 800, a variation of a film producing technique referred to as“chill roll casting” and depicted in FIGS. 1A through 1D, polymer 820 issupplied via tubular member 822 to extrusion head 808. Polymer 820 isheated above its melt point by heater 824 and the melted polymer 810 isthen applied to rotating cylindrical roll 802 (referred to as a “chillroll”) formed of silica or another suitable material. An array ofnanoholes 806 is formed in the circumferential surface 804 of roll 802so as to form a mold, the nanohole array being complementary to thearray of nanofibers to be formed. The nanoholes are formed using methodspreviously described herein. Molten polymer 810 flows into nanoholes 806as it is applied to circumferential surface 804 of rotating chill roll802. Chill roll 802 is maintained at a temperature such that during apredetermined portion of the roll rotation of chill roll 802, polymer810 in nanoholes 806 solidifies along with the portion of polymericmaterial 810 coating circumferential surface 804 of roll 802. Acylindrical metallic roll 812, commonly referred to as a “anvil roll” or“quench roll” functions as the compressing element and is positionedadjacent to chill roll 802 such that after a predetermined angularrotation of chill roll 802 polymeric material 810 coating the surface ofchill roll 802 is compressed between surface 804 of chill roll 802 andsurface 814 of the quench roll 812. As implied by the name “quench roll”polymeric material 810 undergoes rapid cooling during contact withquench/anvil roll 812 so that it may be subsequently stripped from thesurface of chill roll 802 as a continuous elongate strip of film 818.When the polymer strip 818 is removed from chill roll 802, material 810that had previously flowed into nanoholes 806 forms molded nanofibers816 on the surface of film strip 818. In subsequent processing elongatestrips 818 may be slit, cut, chopped or otherwise formed into filterribbons of the present invention. As with the previously described hotpressing method, polymer 820 is not contained in a solution so the useof environmentally undesirable solvents is not required.

Under certain conditions, with suitable polymers, quench roll 812 iseliminated. The thickness of film strip 818 is determined by processparameters, These may include properties of polymer 820, the temperatureof polymer 810 as it is deposited on surface 804 of chill roll 802, thetemperature and rotational speed of chill roll 802, and other factorsthat affect the cooling of film strip 818. Under these conditions,material is drawn into nanoholes 806 of surface 804 of chill roll 802 bysurface tension.

In the methods of manufacture previously herein described, reference ismade to molds made of silica or another suitable material. Among thesesuitable materials are transparent materials like borosilicate glass,soda lime glass, BK7 optical glass, plastic, single-crystal quartz,diamond and sapphire. All have been successfully micromachined withfemtosecond laser pulses. Fused silica is a preferred material since itoffers a combination of properties like wide range of spectraltransparency, low autofluorescence, good biocompatibility, chemicalinertness, near zero thermal expansion, excellent thermal shockresistance, and low dielectric constant and losses.

Any alternate method capable of producing integral arrays of nanofibersof predetermined lengths, diameters, and profiles formed on a surface ofa film and substantially perpendicular to a first surface of a film, andfurther, wherein the spatial arrangement of the fibers has apredetermined pattern, may be used. All fall within the scope of thisinvention.

Using the foregoing methods, nanofiber arrays with a variety ofmechanical, electrical and chemical properties, Debye moments, tailoredaffinities, and functional binding sites can be produced from almost awide variety of polymers without the use of solvents or high voltageelectrical fields.

Nanofibers forming nanofiber arrays disclosed herein can be composed ofvirtually any thermoplastic polymer, polymer resin, or similar material.Non-limiting examples of suitable polymers includepoly(.epsilon.-caprolactone) (PCL), polyethylene oxide (PEO), polyvinylalcohol (PVA), polyvinyl chloride (PVC), polyvinyl formal (PVF),polyisoprene, trans (PI), polypropylene (PP), low-density polyethylene(LDPE), high-density polyethylene (HDPE), PIP castline (PiPc), PIPnatural (PiPn), polyvinylidene fluoride (PVDF), poly-lactic acid (PLA),and poly-L-lactic acid (PLLA). It should be understood that a blend oftwo or more such polymers can also be used. It should also be understoodthat a blend or block co-polymer of two or more such polymers can alsobe used. For example, in one embodiment, a blend of block co-polymercomprising PCL-block-PEO can be used to alter the functionality of thebacking member and nanofibers.

As used herein “ribbon” or “ribbon-like structure” refers to an elongatestrip of flexible polymeric material having an array of nanofibersformed on at least a portion of one of its planar surfaces. Nanofibersare formed on a functional backing material in web form. In a primaryembodiment the webs are post processed by chopping or slitting to formthe ribbon or ribbon like structures. However, for the purposes of thepatent, the entire web may be considered a ribbon or ribbon likestructure.

FIGS. 2A through 7 diagrammatically depict a segment of a filter mediaribbon 100 of the present invention. Ribbon 100 has an elongate planarfilm portion 102 of width 104 and thickness 106, with a first surface108 on which are formed nanofibers 110. In some embodiments, width 104is between 2× and 10× thickness 106. In others width 104 is between 10×and 40× thickness 106. And in yet others width 104 is between 40× and100× thickness 106. Nanofibers 110 have a length 112 and are spaceddistance 114 apart in the longitudinal direction and 116 in thetransverse direction. Nanofibers 110 have a first diameter 120 near thebase of the fiber and decrease in diameter toward the distal end of thefiber. As defined herein the term “nanofiber” refers to a fiberstructure having a diameter of less than 1000 nanometers for more thanhalf the length of the structure. In some embodiments, the nanofibers offilter media of the present invention may have a tapered base portionand a relatively longer fiber portion which extends from the baseportion. Referring now to FIG. 8, nanofiber 210 has a tapered proximalbase portion 201 of diameter 220 with elongate distal portion 203 ofdiameter 222 formed thereon, and a length 212.

Ribbon 100 is depicted with longitudinal distance 114 and transversedistance 116 between adjacent nanofibers 110 constant over surface 108.In other embodiments, either distance 114 or distance 116 or both mayvary along the length of ribbon 100. Nanofibers 110 are shown in orderedparallel rows. In other embodiments other arrangements are useddepending on the particular filtering process requirements. Similarly,height 112 and diameter 120 of nanofibers 110 are constant across thesurface of ribbon 100. In other embodiments height 112 and diameter 120of nanofibers on a first portion of surface 108 of ribbon 100 may havefirst values, while on a second portion of surface 108, height 112 anddiameter 120 may have second values.

The process used to produce nanoholes 806 in chill roll 802 uses theenergy of a single laser pulse to vaporize material so as to form thenanohole. The vaporized material of chill roll 802 is expelled to form ananohole 806. The process is well controlled within limits, however theprecise geometry of a nanohole 806 is determined by the flow ofsuperheated vaporized material at the site. Accordingly, there may beminor variations in the form of nanoholes 806, and in the nanofibers 110that are molded therein. Also, nanofibers 110, particularly those withlong, tendrilous forms, may stretch somewhat during extraction fromnanoholes 806. Therefore it will be understood that when it is statedthat nanofibers 110 in an array have a height 112, height 112 is anominal height, and individual fibers 110 may have a height that issomewhat greater or less than nominal height 112. Similarly, whenconsidering diameters 120 of nanofibers 110, diameter 120 is a nominalvalue and there may be natural variations in the diameters 120 innanofibers 110 within an array.

Nanofibers of the present invention may be broadly characterized by theratio of their length (112 in FIGS. 7 and 212 in FIG. 8) to theiraverage diameter. Typically nanofibers of filter media of the presentinvention have length to diameter ratios between 10:1 and 1,000:1.Nanofibers with length to diameter ratios at the lower end of the rangemay be used in applications in which the fibers require a degree ofstiffness to optimally affect a fluid stream flowing thereby.

The nanofiber arrays formed on filter ribbons of the present inventionmay form a tuned topography. That is ribbons may be optimally configuredto remove specific contaminants such as pathogens, chemicalcontaminates, biological agents, and toxic or reactive compounds from afluid to be filtered. By selecting specific values for longitudinaldistance 114 and transverse distance 116 between adjacent nanofibers(FIGS. 2 through 5), and diameters 120 and 220, and lengths 112 and 212of nanofibers 110 and 200 (FIGS. 7 and 8) ribbons may be formed thatpreferentially remove a specific contaminant. Indeed, filtering devicesmay be formed in which ribbons of a first configuration optimallydesigned for removal of a first contaminant are combined with ribbonsdesigned to remove a second contaminant. Additional ribbons with tunedtopographies for removing specific contaminants may be added to removethese substances from the flow stream. The ribbons may be mixed in afilter device, or formed in discrete layers each containing a singleribbon configuration or a combination of two or more configurations.

Filter media ribbons with nanofibers of the present invention may beformed from virtually any polymeric material. These polymeric materialshave inherent electrostatic properties and exert an electrostatic forceat a point on the surface of an object formed therefrom that isinversely related to the radius of curvature of the surface at thatpoint. As the radius of the surface at a given point is reduced, theelectrostatic attractive force at that point increases. Accordingly, theelectrostatic force exerted by a nanofiber is much greater than thatexerted by a microfiber. This is of particular importance in filterapplications in which contaminants smaller than the pore size of thefilter must be removed from a fluid stream. Electrostatic forces drawcontaminants to fibers for removal from the fluid stream. As thediameter of the fibers is decreased, the electrostatic force exerted bythe fibers increases. The attractive force of a nanofiber is generallyorders of magnitude greater than that of a microfiber, and therein liesthe incentive for creating nanofiber filters. The high level ofelectrostatic force exerted by nanofibers allows them to efficientlyremove contaminants from a fluid stream.

FIGS. 9 and 10 depict field lines 130 and 230 depicting the intensity ofan electrostatic force field line surrounding nanofibers 110 and 210respectively. As described previously, the field intensity at a point onthe surface of a fiber is inversely proportional to the radius ofcurvature of the fiber at that point. This is reflected in the fieldline depicted. It should be noted that the field intensity is maximal atthe distal end of the fibers. In prior art nanofiber filter medialformed by electrospinning or other conventional methods the nanofibersare virtually continuous with length to diameter ratios ranging from1,000,000:1 to 100,000,000. Accordingly, for a given cumulativenanofiber length, fibers of the present invention will have from aboutten to about one thousand times as many fiber ends. The associatedhigher electrostatic potential of nanofiber media formed in accordancewith the present invention allows the construction of filters withefficiencies not attainable using nanofibers formed by electrospinningor other conventional methods.

The arrangement of nanofibers in an array can impact filtrationspecificity and efficiency by modulating the strong gradients in theelectrical and chemical potential fields of normally highly reactivesub-micron length scale structures. Control of these gradients atprocess length scales can enhance efficiency of transport or flow.However, if two nanofibers are in close proximity and the potentialfields overlap, then the gradient of the potential field is reduced andthe advantages of the nanoscale topography are reduced. The arrangementof nanofibers in a nanofiber array of the proper scale and spacing willpreserve the separation of nanofibers thus optimizing the potentialfield gradient.

An electrostatic charge may be imparted to the filter media of thepresent invention to increase the attractive force of the nanofiberarrays formed on ribbons. Filter ribbons of the present invention may beformed from a polymer or polymer blend with suitable electretproperties. Among these materials are polypropylene, poly(phenyleneether) and polystyrene. In certain embodiments these ribbons may have alamellar construction that has a first layer formed of an electretmaterial on which are formed nanofiber arrays of the present invention,and a second layer bonded thereto with desirable physical and/orelectrical properties. The materials selected for each layer may beoptimized for a specific filtering application. Charging of the mediamay be accomplished by corona discharge, triboelectrification,polarization, induction, or another suitable method. Over time theimparted electrostatic charge may be dissipated by particle loading,and/or by quiescent or thermal stimulation decay.

Nanofiber arrays on media ribbons of the present invention alsoadvantageously affect the wetting of the surface of the ribbon by watervapor. Many polymers are hydrophobic, or have low wetting ability. Thepresence of nanofiber arrays of the present invention on the surface ofa polymeric filter element increases the wettability of the surface sothat vapor precipitates and collects on the filter media. Nano-texturednucleation of the liquid from the vapor is triggered by the tips of thenanofibers. Droplets grow to cover the surface of the media once acritical radius is reached. This wetting of the nanofiber array coveredsurface enhances the collection efficiency of the element. This isdiagrammatically illustrated in FIGS. 11 and 12. FIG. 11 is a sectionalview of a polypropylene element 300 with a substrate 302 on which afirst portion 305 of the upper surface has formed thereon an array ofnanofibers 310 of the present invention, and a second surface portion303 does not have nanofibers. In FIG. 12A oil droplet 307 partially wetsportion 303, while on the portion 305 with nanofibers 310 wetting of thesurface by oil 309 is complete. By contrast, in FIG. 12B, the wetting offirst portion 303 by oil droplet 307 is low, and the wetting of secondportion 305 by oil 309 is lessened by nanofibers 310 as shown byspherical droplet 309 formed on nanofibers 310.

Methods for modifying the wettability of surfaces by forming nanofiberarrays thereon are discussed in detail in co-pending application U.S.2020/0039122 herein incorporated by reference in its entirety.

Referring now again to FIGS. 2 through 6, because the nanofibers onmedia ribbons of the present invention are not structural members, butrather formed on a surface of a ribbon that serves as a structuralmember, width 104 and thickness 106 of planar film portion 102 of ribbon100 may be selected for ease of processing and filter flowconsiderations. The thickness 106 and width 104 of planar film portion102 must be sufficient to allow subsequent processing, and must allowfor the efficient formation of nanofibers 110 on film 102. Within theseconstraints it may be desirable to minimize 104 so as to reduce theresistance to fluid flow through the filter element formed. Ribbon 100is formed as a continuous elongate element that may be cut to length asrequired during processing.

Woven filter media may be created from ribbons 100. The ribbons may beweaved individually in the structure, or may be formed into amulti-strand yarn prior to weaving. Alternatively, ribbons 100 can beformed into a non-woven mat 400 as depicted in FIG. 13. The orientationof ribbons 402 in mat 400 may be random, or may have a preferentialorientation in which the nanofiber bearing surfaces of ribbons 402 lieat low angles to the direction of flow, the orientation beingestablished during manufacture of mat 400.

Referring now to FIG. 14A, respirator mask 420 achieves high filteringefficiency and low pressure drop through use of filter ribbons of thepresent invention. As depicted in FIG. 14B, mask 420 has a first outerlayer 422 formed of ribbons of a hydrophobic polymer such as, forexample, polypropylene. The ribbons forming first layer 422 have formedon them arrays of nanofibers configured to maximize the hydrophobicnature of the material. First layer 422 is preferably a woven ornon-woven fabric. Second layer 424 is formed of microfibers configuredto filter micron-sized coarse particles and some submicron-particles inthe fluid stream. Microfibers of second layer 424 may be made ofpolyethylene, glass, cellulose acetate, activated carbon fiber orcombinations thereof. Optionally second layer 424 may also containnanofiber bearing filter ribbons of the present invention with thenanofiber arrays configured to optimally remove contaminants of a firstcomposition or size. Third layer 426 is a non-woven mat formed ofnanofiber bearing filter ribbons of the present invention. Because theribbons from which this layer are formed have structural strength, thenon-woven mat has a predetermined thickness and flow characteristicsselected for optimal removal of contaminants while preserving airflow atlow pressure drop and resistance to clogging. The arrays of nanofiberson these ribbons are optimally configured for the removal of smallparticles. Because of the higher attractive electrostatic forces of thenanofiber arrays compared to other filter elements with continuousrandom fibers, filter layer 426 is able to draw contaminants greaterdistances for removal from the fluid stream. In certain embodimentsnanofiber arrays of ribbons forming third layer 426 may be configured topreferentially remove specific contaminants. Indeed, additional layersof ribbon mats of the present invention may be positioned proximal tothis third layer, the nanofiber arrays of each layer being optimized toremove specific contaminants. Proximal to the previously describedfilter layers is permeable layer 428 formed of a fabric, woven ornon-woven that may, in some embodiments, be comfortably pressed againstthe face of the wearer. In masks of the present invention, the filterlayers are not bonded to each other. In production, the layers formingthe filter assembly may be produced as continuous sheets of material,laid up in the proper order, and then bonded together in selectedlocations thermally, by a glue or solvent bonding, by stitching, or byneedle punch, a joining method for non-woven fabrics. Because nanofibersof the present invention are integrally formed on the surface of ribbonsof the present invention, the nanofibers cannot become loose and beinhaled by the wearer as is possible with respirators made with priorart filter assemblies.

Advantageously, for certain applications like mask 420, nanofiberbearing ribbons of the present invention may be formed of anantimicrobial plastic. Representative of these materials is MICROBAN® byMicroban, Inc. (Huntersville, N.C.). MICROBAN® is a synthetic polymermaterial containing an integrated active ingredient which makes iteffective against microbial growth. The MICROBAN® additive may beblended with polymers with optimal properties for forming nanofiberarrays in methods herein described to create filter ribbons of thepresent invention that not only have the ability to efficiently removemicrobes from a fluid stream, but also to kill those microbes. Incertain embodiments these ribbons have a lamellar construction wherein afirst layer, on which are formed nanofiber arrays of the presentinvention, is bonded to a second layer with optimal physical properties,the first layer being formed of an antimicrobial plastic.

Prior art filter media formed of nanofibers are primarily made byelectrospinning or a similar method that forms a thin, membrane-likefiber mat. Flow through the structure is substantially normal to theplane of the mat, and, because the fibers are not substantiallydistanced one from another in a direction normal to the plane of themat, clogging may limit the filter life and efficiency. In contrast,filter media of the present invention comprises ribbons withcross-sections orders of magnitude greater than nanofibers. This allowsthe construction of filters wherein the media ribbons are spaced onefrom another so as to create a resilient three-dimensional structure.Because the fibers are so spaced, flow through the filter media is notrestricted to a single direction. Indeed, a suitable housing may befilled with ribbons of the present invention and flow may proceed from adefined inlet to a defined outlet with the path therebetween beingundefined. Indeed, baffles may be added to lengthen the path for flowthrough the media. In filter media of the present invention thenanofibers are not structural members but rather are features on astructural members, these features being configured to create attractiveelectrostatic forces that are orders of magnitude greater than thosecreated by filter elements wherein the nanofibers are structuralmembers. Particles suspended in a fluid exhibit random motion resultingfrom their collisions with fast-moving fluid molecules, an effect knownas “Brownian Motion”. Filter elements formed of ribbons of the presentinvention create flow paths that are orders of magnitude longer thanthose of prior art membrane-like nanofiber filter elements. These longerflow paths take advantage of the Brownian Motion effect to allow thebuilding of filters that have a high filtering efficiency combined witha low pressure drop, and the added benefit of an increased resistance toclogging.

FIG. 15 depicts a filter 500 wherein media 502, formed of media ribbonsof the present invention, is contained within a housing 504 with aninlet 506 and an outlet 508. Housing 504 has formed therein baffles 510that form a labyrinthian flow path between inlet 506 and outlet 508. Thelong flow path through media 502 exploits the Brownian Motion effect tomaximize interaction between contaminants and the electrostatic fieldcreated by nanofiber arrays on ribbons of media 502. Filter 500illustrates the design flexibility that is enabled by filter ribbons ofthe present invention. While prior art nanofiber filter elements haveonly a simple flow path with the limitations previously hereindescribed, filter media formed of ribbons of the present invention maybe utilized in substantially the same manner as conventional microfibermedia.

While filter element ribbons and ribbon segments of the presentinvention have been previously described and depicted with flat filmportions, other shapes are contemplated and fall within the scope ofthis invention. For instance, ribbon 600 depicted in FIGS. 16A and 16Bhas a film portion 602 that is folded longitudinally during manufacture.As depicted, the fold remains closed with the film halves 603 beingessentially parallel. In other embodiments film halves 603 are angularlyoriented one to another due to spring-back of the material afterfolding. This angular orientation may be as great as 150 degrees incertain embodiments.

FIGS. 17A and 17B depict ribbon 700 in which the film portion 702 isgiven a form similar to a hollow fiber during manufacture. Nanofibers710 protrude radially outward from film portion 702. In some embodimentsedges 705 of film portion 702 may meet to form a complete cylindricalbody. In others they may be separated by distances that approach theinner diameter of the formed ribbon.

Unlike prior art processes for producing nanofibers filter media, thechill roll casting process previously herein described is scalable andmay be automated to enable production of quantities of nanofiber-bearingfilter ribbons rapidly and at low cost. For instance, referring now toFIGS. 18 and 19 depicting chill roll casting system 800 (FIGS. 1Athrough 1D), slitting of film strip 818 may accomplished automaticallyby adding a slitting means as depicted in FIG. 18. Subsequent to theremoval of film strip 818 from chill roll 802, a plurality of slits 842are formed in strip 818 so as to form a plurality of filter ribbons 819of the present invention as depicted in region 840 of FIG. 18. Ribbons818 are analogous in form and function to elongate ribbons 100 depictedin FIGS. 2 through 7. However, in other embodiments (not shown), theslitting means may be placed adjacent the chill roll 802 and configuredto form a plurality of slits in the cooled polymer covering the chillroll 802 before removing the film strip 818 from chill roll 802. Theslitting may be accomplished by mechanical means using a rotatingcylindrical cutting element with a plurality of sharpenedcircumferential cutting edges formed on its cylindrical surface, and asecond rotating cylinder. The axes of both cylinders are parallel to theaxis of chill roll 804, and are positioned such that the cutting edgesof the cutting element contact or are in very close proximity to thesurface of the second rotating cylinder. Strip 818 passes between thisrotating cutting element and the second cylinder so that each cuttingedge forms a continuous longitudinal slit 842 in strip 818. Slitting offilm material in this manner is well known in the art.

In the casting system of FIGS. 18 and 19 longitudinal slits 842 areformed in strip 818 automatically as strip 818 is produced. In othermethods of the present invention, slitting of strip 818 is done as asecondary process remote from the system 800. Strip 818 can be woundonto a spool for storage and subsequent slitting. In the previousexample, longitudinal slits 842 were formed in strip 818. In othermethods for making filter ribbons of the present invention, lateralslits are made to form ribbons. Indeed, any method of cutting, slittingor chopping a film strip on which nanofiber arrays are formed may beused to form filter ribbons of the present invention. All fall withinthe scope of this invention.

In some embodiments, filter media ribbons of the present invention aredivided into segments of predetermined length. These segments may beformed into non-woven mats or placed in a housing as previouslydescribed.

FIGS. 20 and 21 depict the chill roll system of FIGS. 18 and 19 with ameans added for automatically cutting ribbons 819 into short segments900 depicted in FIGS. 22 through 24. Lateral cuts 852 are formed inribbons 819 by a rotating cylindrical cutting element with axiallyoriented cutting edges formed on the circumferential surface of theelements. As with the forming slits 842 in strip 818, lateral cuts areformed by cooperative action between the cylindrical cutting element anda second cylinder as previously described. Transection of strip 818 bylateral cuts 852 creates a plurality of segments 900, length 905 ofsegment 900 being determined by the spacing of cutting edges on thecylindrical cutting element.

Segment 900 is identical to ribbon 100 in all aspects except asspecifically hereafter described. Like ribbon 100, segment 900 hasarrays of nanofibers 910 formed on first surface 908 of film portion902. However, segment 900 has a predetermined length 905. In someembodiments length 905 is 100× or greater than width 904 of ribbon 900.In other embodiments, length 905 is between 10× and 100× width 904 ofribbon 900. In yet other embodiments, length 905 is between 1× and 10×width 904 of ribbon 900. The length of a segment for an application maybe optimized based on filtering requirements and on the method ofmanufacturing the filter. For instance, if the filter will incorporate anon-woven mat formed of segments 900, it may be advantageous to makelength 905 a higher multiple of width 904 than would be the case ifsegments 900 were to fill a cavity in a housing.

In certain embodiments ribbon segments may have a shape imparted to thefilm portion so that when the segments are assembled in a non-woven mator into a filter housing, natural flow paths between segments arecreated. Referring now to FIGS. 25 through 27, segment 1000 is likesegment 900 with an array of nanofibers 1010 formed on first surface1108 of film portion 1002. Film portion 1002 is not flexibly planar asin previously described embodiments, but rather has a form impartedthereto during manufacture. Forming of film portion 1002 in the mannerdepicted for segment 1000 may also be advantageously applied to elongatefilter ribbons of the present invention so as to aid in the creation offlow paths through the assembled filter element.

When viewed in a plan view, ribbon segments 900 and 1000 have arectangular shape imparted by the orthogonal cuts that formed them. Inother embodiments formed by other slitting, cutting or chopping methods,the shape of the ribbon segments may have other predetermined shapes, ormay be randomly formed segments with irregular shapes. All fall withinthe scope of this invention.

FIGS. 28 through 31 depict a chill casting system of the presentinvention for making a layered film for forming filter ribbons of thepresent invention. Polymer 1120 is supplied via tubular member 1122 toextrusion head 1108. Polymer 1120 is heated above its melt point byheater 1124 and the melted polymer 1110 is then applied to rotatingchill roll 1102. Molten polymer 1110 flows into nanoholes 1106 as it isapplied to circumferential surface 1104 of rotating chill roll 1102.Polymer film 1130 is drawn into the juncture between quench roll 1112and cylindrical surface 1108 of chill roll 1104 upon which meltedpolymer 1110 has been deposited. Quench roll 1112 cools molten polymer1110 in the manner previously described, but also forms a bond betweenfilm 1130 and polymer 1110 so that when film strip 1118 is removed fromchill roll 1104 as a layered construct with a first layer on which areformed nanofiber arrays of the present invention, and a second layerformed of film 1130. In this manner film and the filter ribbons fromwhich they are formed may have nanofiber arrays formed of a firstpolymeric material 1110 with optimal filtering or wetting properties fora given application, bonded to a second polymeric material forming film1130. Forming a construct in this manner allows polymers with optimalproperties for nanofiber formation and/or filtering to be bonded topolymer films that have optimal properties for filter production.

In an alternate system for making films with nanofiber arrays forproducing filter ribbons of the present invention, nanofibers areembossed on an existing film of polymeric material, the embossing beingaccomplished in a process similar to the chill casting method previouslyherein described. In previous embodiments a molten polymer is applied tothe mold. In the embossing embodiment film is applied to the mold; thefilm is sufficiently heated to allow the material to flow into the moldnanoholes, then cooled so that the film with its newly formed nanofiberscan be peeled from the mold. Referring now to FIGS. 32 and 33 depictingan embossing system 1200 of the present invention, film 1280 wrapsaround circumferential surface 1204 of mold 1202 wherein are formednanoholes 1206. Film 1280 is heated by airflow 1272 from nozzle 1270sufficiently to melt or sufficiently softened to allow film material toflow into nanoholes 1206. Quench roll 1212 applies a compressive forceto softened film 1280 that assists with the flow of film material intonanoholes 1206. Chilled air 1278 from nozzle 1276 cools film 1280 sothat chilled film 1282 with nanofibers 1284 can be peeled fromcylindrical surface 1204 of chill roll 1202. Film 1282 is like film 818with nanofibers 816 formed by casting system 800 (FIGS. 18 to 21) in allaspects of form and function. Layered films with embossed nanofibers mayalso be made by a method similar to that previously described anddepicted in FIGS. 28 through 31. In the embossing method a second filmis drawn into the juncture between quench roll 1212 and film 1280 so asto bond film 1280 to the second film. System 1200 uses heated airflow toincrease the temperature of film so that film material can flow intonanoholes. In other embodiments film 1280 is heated by a radiant heateror other suitable means.

In other embodiments, film 1280 is formed of a malleable polymer that isapplied to surface 1204 of mold/chill roll 1202 such that the malleablepolymer film 1280 infiltrates at least a portion of nanoholes 1206. Roll1212 is maintained at a temperature such that compressive force appliedby roll 1212 to film 1280 causes further infiltration of film 1280 intonanoholes 1206 and solidification of that material and of materialcovering surface 1204 of chill roll 1202. Thereafter, film 1282 withnanofibers 1284 formed thereon is removed from roll 1202 in the mannerpreviously described.

Filter media of the present invention provide the benefits of nanofibersin elongate ribbons that can be subsequently processed in largely thesame manner as conventional fibrous filter media. Filter media of thepresent invention are not deposited on a substrate during manufacturingand are configured to maximally exploit the electrostatic properties ofthe materials from which they are formed. Along with enhancedelectrostatic properties, the nanofibers arrays of ribbons may affectthe wettability of the ribbon surface on which they are formed.Wettability for selected liquids may be preferentially enhanced whiledecreasing the wettability for other liquids thereby increasing filterefficiency. Because the nanofiber arrays are integral with the ribbonthey cannot be expelled from the filter media. Ribbons or the presentinvention with nanofibers integrally formed thereon may be produced atreduced cost compared to conventionally produced nanofiber media, andwithout the use of high voltage or environmentally detrimental solvents.

According to the principles of the present invention, any flexibleelongate ribbon-like polymeric structure having arrays of nanofibersformed on at least one surface falls within the scope of this inventionregardless of the method of manufacture of the structure.

Although embodiments of the present invention have been described indetail, it will be understood by those skilled in the art that variousmodifications can be made therein without departing from the spirit andscope of the invention as set forth in the appended claims.

This written description uses examples to disclose the invention andalso to enable any person skilled in the art to practice the invention,including making and using any devices or systems and performing anyincorporated methods. The patentable scope of the invention is definedby the claims, and may include other examples that occur to thoseskilled in the art. Such other examples are intended to be within thescope of the claims if they have structural elements that do not differfrom the literal language of the claims, or if they include equivalentstructural elements with insubstantial differences from the literallanguages of the claims.

It will be understood that the particular embodiments described hereinare shown by way of illustration and not as limitations of theinvention. The principal features of this invention may be employed invarious embodiments without departing from the scope of the invention.Those of ordinary skill in the art will recognize numerous equivalentsto the specific procedures described herein. Such equivalents areconsidered to be within the scope of this invention and are covered bythe claims.

All of the compositions and/or methods disclosed and claimed herein maybe made and/or executed without undue experimentation in light of thepresent disclosure. While the compositions and methods of this inventionhave been described in terms of the embodiments included herein, it willbe apparent to those of ordinary skill in the art that variations may beapplied to the compositions and/or methods and in the steps or in thesequence of steps of the method described herein without departing fromthe concept, spirit, and scope of the invention. All such similarsubstitutes and modifications apparent to those skilled in the art aredeemed to be within the spirit, scope, and concept of the invention asdefined by the appended claims.

Thus, although there have been described particular embodiments of thepresent invention, it is not intended that such references be construedas limitations upon the scope of this invention except as set forth inthe following claims.

1. A method for making polymeric objects having a surface on which isformed an array of nanofibers, the method comprising: providing a firstcylindrical roll with an array of nanoholes formed in a circumferentialsurface thereof; providing a source of moldable polymer; rotating thefirst cylindrical roll; applying the moldable polymer to the rotatingfirst cylindrical roll at a first angular location so that the moldablepolymer covers at least a portion of the circumferential surface of therotating first cylindrical roll and infiltrates at least a portion ofthe nanoholes; cooling the moldable polymer while rotating the coveredfirst cylindrical roll to a second angular position; and removing thecooled polymer applied to the first cylindrical roll from the firstcylindrical roll as an elongate film; wherein the polymer thatinfiltrated the nanoholes forms the array of nanofibers on a surface ofthe elongate film.
 2. The method of claim 1, wherein the firstcylindrical roll is maintained at a temperature that causes the moldablepolymer to solidify in the nanoholes along with a portion of themoldable polymer covering the circumferential surface of the firstcylindrical roll after a predetermined angular rotation of the firstcylindrical roll.
 3. The method of claim 1, further comprising a secondcylindrical roll with an axis parallel to the first cylindrical roll,wherein the second cylindrical roll is positioned adjacent to the firstcylindrical roll such that after a predetermined angular rotation of thefirst cylindrical roll, the polymer covering the first cylindrical rollis compressed in a space between the circumferential surface of thefirst cylindrical roll and a circumferential surface of the secondcylindrical roll.
 4. The method of claim 3, wherein the secondcylindrical roll is maintained at a temperature that causes the moldablepolymer to solidify in the nanoholes along with a portion of themoldable polymer covering the circumferential surface of the firstcylindrical roll after the polymer passes through the space.
 5. Themethod of claim 3, further comprising: providing a source of polymerfilm; and feeding the polymer film into the space between thecircumferential surface of the first cylindrical roll and thecircumferential surface of the second cylindrical roll while rotatingthe covered first cylindrical roll to the second angular position sothat the polymer film is compressed in the space with the moldablepolymer covering the first cylindrical roll to join the polymer film toat least a portion of the moldable polymer covering the circumferentialsurface of the first cylindrical roll; wherein removing the cooledpolymer from the first cylindrical roll as an elongate film is removingthe joined polymer film and cooled polymer from the first cylindricalroll as an elongate layered construct after the joined polymer film andcooled polymer pass through the space; and wherein the polymer thatinfiltrated the nanoholes forms the array of nanofibers on a surface ofthe elongate layered construct.
 6. The method of claim 5, wherein theelongate layered construct comprises: a first layer having a firstsurface on which is formed the array of nanofibers; and a second layerfixed to a second surface of the first layer; wherein: the first layeris formed of the cooled polymer removed from the first cylindrical roll,and the second layer is formed of the polymer film.
 7. The method ofclaim 5, wherein: the moldable polymer is formed from a first polymericmaterial; and the polymer film is formed from a second polymericmaterial different from the first polymeric material.
 8. The method ofclaim 3, wherein: the moldable polymer is a first polymer film; and themethod further comprises heating the polymer film to a temperature thatcauses the heated polymer film covering the first cylindrical roll toflow into at least a portion of the nanoholes when the heated polymerfilm is compressed in the space between the circumferential surface ofthe first cylindrical roll and a circumferential surface of the secondcylindrical roll.
 9. The method of claim 8, further comprising:providing a source of second polymer film; and feeding the secondpolymer film into the space between the circumferential surface of thefirst cylindrical roll and the circumferential surface of the secondcylindrical roll while rotating the covered first cylindrical roll tothe second angular position so that the first and second polymer filmsare compressed in the space to join the second polymer film to at leasta portion of the first polymer film covering the circumferential surfaceof the first cylindrical roll; wherein removing the cooled polymer fromthe first cylindrical roll as an elongate film is removing the joinedsecond polymer film and cooled first polymer film from the firstcylindrical roll as an elongate layered construct after the first andsecond polymer films pass through the space; and wherein the polymerthat infiltrated the nanoholes forms the array of nanofibers on asurface of the elongate layered construct.
 10. The method of claim 1,further comprising: providing a means for slitting the cooled polymercovering the first cylindrical roll; forming a plurality of slits in thecooled polymer covering the first cylindrical roll before removing thecooled polymer from the first cylindrical roll; and removing the cooledpolymer from the first cylindrical roll as a plurality of elongateribbons; wherein the polymer that infiltrated the nanoholes forms thearray of nanofibers on a surface of each elongate ribbon of theplurality.
 11. The method of claim 1, further comprising: forming aplurality of slits in the elongate film; and separating the elongatefilm into a plurality of ribbons.
 12. A method for making polymericobjects having a surface on which is formed an array of nanofibers, themethod comprising: providing a rotating mold with an array of nanoholesformed in a circumferential surface thereof; applying a flowable polymerto the rotating mold at a first angular location so that the flowablepolymer coats at least a portion of the circumferential surface of therotating mold and infiltrates at least a portion of the nanoholes;cooling the flowable polymer while the coated rotating mold rotates to asecond angular position; and removing the cooled polymer from therotating mold as an elongate film; wherein the polymer that infiltratedthe nanoholes forms the array of nanofibers on a surface of the elongatefilm.
 13. The method of claim 12, wherein the rotating mold ismaintained at a temperature that causes the flowable polymer to solidifyin the nanoholes along with a portion of the flowable polymer coatingthe circumferential surface of the rotating mold after a predeterminedangular rotation of the mold.
 14. The method of claim 12, furthercomprising a compressing element positioned adjacent to the rotatingmold such that after a predetermined angular rotation of the rotatingmold, the polymer coating the mold is compressed in a space between thecircumferential surface of mold and a surface of the compressingelement.
 15. The method of claim 14, wherein the compressing element ismaintained at a temperature that causes the flowable polymer to solidifyin the nanoholes along with a portion of the polymer coating thecircumferential surface of the rotating mold after the polymer passesthrough the space.
 16. A method for making polymeric objects having asurface on which is formed an array of nanofibers, the methodcomprising: providing a mold with an array of nanoholes formed in asurface thereof, applying a malleable polymer to the mold so that themalleable polymer covers at least a portion of the surface of the moldand infiltrates at least a portion of the nanoholes; compressing themalleable polymer against the surface of the mold with a compressingelement maintained at a temperature that causes the malleable polymer tosolidify in the nanoholes along with a portion of the polymer coveringthe surface of the mold; removing the solidified polymer from the moldas a film; wherein the polymer that infiltrated the nanoholes forms thearray of nanofibers on a surface of the film. 17-29. (canceled)